A glucose screening test is a routine test during pregnancy that checks a pregnant woman’s blood glucose (sugar) level.
A glucose tolerance test is done if a glucose screening test result is higher than normal. It is used to diagnose gestational diabetes.
Gestational diabetes is high blood sugar (diabetes) that starts or is found during pregnancy.
For the glucose screening test:
If your blood glucose is too high, you will need to come back for a glucose tolerance test. For this test:
Eat your normal foods in the days before your test. Ask your health care provider if any of the medicines you take can affect your test results.
Most women do not have side effects from the glucose tolerance test. Some may feel nauseated, sweaty, or light-headed after they drink the glucose solution. Serious side effects from this test are very uncommon.
Most pregnant women have a glucose screening test between 24 and 28 weeks of pregnancy. This test checks for gestational diabetes. The test may be done earlier if you have high glucose levels in your urine during your routine prenatal visits or if you have a high risk for diabetes.
Women who have a low risk for diabetes may not have the screening test. To be low-risk, all of these statements must be true:
Most of the time, a normal result for the glucose screening test is a blood sugar that is equal to or less than 140mg/dL 1 hour after drinking the glucose solution. A normal result means you do not have gestational diabetes.
Note: mg/dL means milligrams per deciliter. It is a way to indicate how much glucose is in the blood.
If your blood glucose is higher than 140 mg/dL, the next step is the oral glucose tolerance test. This test will show if you have gestational diabetes. Most women (about 2 out of 3) who take this test do NOT have gestational diabetes.
Abnormal blood values for a 3-hour 100-gram oral glucose tolerance test are:
If only 1 of your blood glucose results in the oral glucose tolerance test is higher than normal, your health care provider may simply suggest you change some of the foods you eat. Then, your health care provider may test you again after you have changed your diet.
If more than 1 of your blood glucose results is higher than normal, you have gestational diabetes.
Oral glucose tolerance test - pregnancy (OGTT); Glucose challenge test - pregnancy
Gestational diabetes mellitus. Practice Bulletin NO. 137. American College of Obstetricians and Gynecologists. Obstet Gynecol. 2013:122:406-16.
London MB, Catalano PM, Gabbe SG. In: Gabbe SG, Niebyl JR, Simpson JL, et al, eds. Obstetrics: Normal and Problem Pregnancies. 6th ed. Philadelphia, PA: Saunders Elsevier; 2012:chap 39.
Updated by: Cynthia D. White, MD, Fellow American College of Obstetricians and Gynecologists, Group Health Cooperative, Bellevue, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
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